1. Field of the Invention
The present invention generally relates to an optical pickup having a light guide path element in which a light guide path is laminated on a substrate, and more particularly to an optical pickup which can commonly use two wavelengths different from each other.
2. Description of the Related Art
Recently, in addition to a CD (Compact Disc) or CD-R (CD-Readable), which have been conventionally utilized as an optical disc, a DVD is getting popular which can improve the record density, so that the usage of the optical pickup necessary for those different types of discs becomes various. While the CD or the CD-R utilizes a laser light whose wavelength is about 780 nm, the DVD utilizes a laser light whose wavelength is about 650 nm. Thus, different optical pickups are employed for those different wavelengths. In order to reduce the cost and miniaturize the apparatus, an optical pickup is desired which can be commonly used for the CD or CD-R and the DVD.
However, there is a problem that a structure of an optical system in the above-mentioned desired optical pickup commonly usable for two different wavelengths becomes complicated, resulting in that the cost is increased and the miniaturization of the optical pickup becomes difficult.
On the other hand, a light guide path element, to which the integrated circuit technology is adapted, is being developed nowadays. If such a light guide path element is adapted to the optical pickup, since elements having various functions can be integrated in a multiple-layered structure, it is possible to realize an optical pickup which is small and reliable.
However, in case that an optical pickup usable for two different wavelengths is constituted by using such a light path element, since the light sources for the respective wavelengths are disposed separately, it is difficult to couple and transmit the light beams, which are emitted from respective light sources, and to irradiate the light beams onto an information record medium through a common optical system. Furthermore, in case of reproducing the CD or DVD, it is necessary to perform the focusing servo control and the tracking servo control. These servo controls may not be always the same for various types of the discs such as the CD and the DVD. For example, as for the tracking servo control, the 3-beams method may be employed for the CD while the ordinary phase different method may be employed for the DVD. In such a case, the structure of the grating and the light receiving portions become complicated, resulting in that it is difficult to couple them with the light guide path element.
It is therefore an object of the present invention to provide a light guide path element, which can be commonly used for information record mediums corresponding to two different wavelengths, can have a rather simple structure and can be rather easily miniaturized, and also provide an optical pickup having such an optical guide path element.
The above object of the present invention can be achieved by a light guide path element provided with: a first light guide path for guiding a light beam having a first wavelength; a second light guide path for guiding a light beam having a second wavelength; a first separating device for irradiating the light beam having the first wavelength irradiated from a first light source onto an information record medium and transmitting a light beam reflected therefrom; a second separating device for irradiating the light beam having the second wavelength irradiated from a second light source onto an information record medium and transmitting a light beam reflected therefrom; a first grating for input-coupling one portion of the light beam transmitted through the first separating device to the first light guide path and transmitting another portion of the light beam transmitted through the first separating device; a second grating for input-coupling one portion of the light beam transmitted through the second separating device to the second light guide path and transmitting another portion of the light beam transmitted through the second separating device; a first light receiving portion for receiving the light beam transmitted through the first grating or the second grating; a second light receiving portion for receiving the light beam guided by the first light guide path; and a third light receiving portion for receiving the light beam guided by the second light guide path.
According to the light guide path element of the present invention, the light beam having the first wavelength is emitted from the first light source, and is irradiated onto the information record medium by the first separating device. Then, the reflected light beam is transmitted through the first separating device and reaches the first grating. Then, one portion of this light beam is input-coupled to the first wave guide path while another portion of this light beam is transmitted and is received by the first light receiving portion. The light beam guided by the first wave guide path is received by the second light receiving portion.
On the other hand, the light beam having the second wavelength is emitted from the second light source, and is irradiated onto the information record medium by the second separating device. Then, the reflected light beam is transmitted through the second separating device and reaches the second grating. Then, one portion of this light beam is input-coupled to the second wave guide path while another portion of this light beam is transmitted and is received by the first light receiving portion. The light beam guided by the second wave guide path is received by the third light receiving portion.
Therefore, it is possible to irradiate the light beams having two different wavelengths onto the information record medium and guide the light beams by the different wave guide paths respectively, so that a light guide path element commonly usable for the two wavelengths (e.g., for the CD or the DVD), which is suitable for miniaturization and whose structure is simplified, can be realized.
In one aspect of the light guide path element of the present invention, at least one of the first separating device and the second separating device is provided with a light guide path having a grating for input-coupling the light beam and a grating for output-coupling the light beam so as to irradiate the light beam onto the information record medium.
According to this aspect, at least one of the first separating device and the second separating device input-couples the light beam from the light source by one grating and, after the light beam is guided by the light guide path, irradiates the light beam onto the information record medium by another grating. Therefore, regardless of the position of the information record medium, by designing one grating for input-coupling in correspondence with the position of the light source and also designing another grating for output-coupling in correspondence with the optical axis of the light beam, a light guide path element commonly usable for the two wavelengths, whose degree of freedom as for the arrangement is high and whose structure is rather simple and suitable for the miniaturization, can be realized.
In another aspect of the light guide path element of the present invention, at least one of the first separating device and the second separating device is provided with a separation film laminated on the first and second light guide paths for selectively reflecting and transmitting the light beam in correspondence with a phase difference given to the light beam.
According to this aspect, one of the first separating device and the second separating device reflects the light beam from the light source by the separation film, which is laminated on the light guide path element, toward the information record medium, and transmits the reflected light beam while giving the phase difference to the reflected light beam. Therefore, it is possible to construct the separating device without equipping the light guide path or the grating, so that a light path element commonly usable for the two wavelengths, whose structure is rather simple and suitable for the miniaturization, can be realized.
In another aspect of the light guide path element of the present invention, the first separating device generates three beams by diffracting the light beam having the first wavelength so that a tracking error signal is generated by use of the three beams on the basis of a light reception output of the third light receiving portion.
According to this aspect, when the light beam having the first wavelength is inputted to the first separating device, it is diffracted so that the three beams are generated in the light guide path surface. Then, the tracking error signal is generated on the basis o the light reception output of the third light receiving portion by use of those three light beams. Therefore, a light path element commonly usable for the two different wavelengths, which can easily perform the tracking error detection by means of the 3-beams method typically used for the CD, can be realized.
In another aspect of the light guide path element of the present invention, each of the first grating and the second grating are divided into two areas so that a focus error signal is generated by a beam size method by the light beam transmitted through one of the two areas and the light beam transmitted through another of the two areas at the second light receiving portion and the third light receiving portion.
According to this aspect, the light beam having the first wavelength is transmitted through the first grating which is divided into two areas, so that the focus error signal by means of the beam size method is generated in the second light receiving portion. The light beam having the second wavelength is transmitted through the second grating which is divided into two areas, so that the focus error signal by means of the beam size method is generated in the third light receiving portion. Therefore, a light guide path element, which can cope with the focus error detection for the optical disc, by designing the grating pattern, can be realized.
In another aspect of the light guide path element of the present invention, the first wavelength is 650 nm and the second wavelength is 780 nm.
According to this aspect, the light beam having the wavelength of 650 nm for the DVD and the light beam having the wavelength of 780 nm for the CD or the CD-R can be commonly used. Therefore, a light guide path element commonly usable for the DVD and the CD i.e., the typical optical discs capable of high density recording, whose structure is rather simple and suitable for the miniaturization, can be realized.
The above object of the present invention can be also achieved by an optical pickup having the above described light guide path element of the present invention (including the various aspects thereof, wherein an RF signal is generated on the basis of a light reception output of the first light receiving portion, and a focus error signal is generated on the basis of a light reception output of the second light receiving portion and a light reception output of the third light receiving portion.
According to the optical pickup of the present invention, the light beam having the first wavelength is emitted from the first light source, and is irradiated onto the information record medium by the first separating device. Then, the reflected light beam is transmitted through the first separating device and reaches the first grating. Then, one portion of this light beam is input-coupled to the first wave guide path while another portion of this light beam is transmitted and is received by the first light receiving portion. The light beam guided by the first wave guide path is received by the second light receiving portion. Then, the RF signal is generated on the basis of the light reception output of the first light receiving portion while the focus error signal is generated on the basis of the light reception output of the second light receiving portion.
On the other hand, the light beam having the second wavelength is emitted from the second light source, and is irradiated onto the information record medium by the second separating device. Then, the reflected light beam is transmitted through the second separating device and reaches the second grating. Then, one portion of this light beam is input-coupled to the second wave guide path while another portion of this light beam is transmitted and is received by the first light receiving portion. The light beam guided by the second wave guide path is received by the third light receiving portion. Then, the RF signal is generated on the basis of the light reception output of the first light receiving portion while the focus error signal is generated on the basis of the light reception output of the third light receiving portion.
Therefore, it is possible to irradiate the light beams having two different wavelengths onto the information record medium and guide the light beams by the different wave guide paths respectively, so that an optical pickup commonly usable for the two wavelengths (e.g., for the CD or the DVD), which is suitable for miniaturization and whose structure is simplified, can be realized.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.